1. Field of the Invention
The present invention generally relates to a cryogenic refrigerator which generates cold (a cold thermal energy causing an ultracold temperature) by generating Simon expansion using a high pressure refrigerant gas supplied from a compression device.
2. Description of the Related Art
Patent Document 1 discloses that a clearance sealing mechanism is provided on an outer peripheral surface of a second stage displacer on a high temperature side and a helical groove is provided on the outer peripheral surface on the side other than the high temperature side. With this structure, a surface heat pumping function of a refrigerant gas inside the helical groove is used for refrigeration of a refrigerator.    [Patent Document 1] Japanese Patent No. 3851929